U.S. Pat. No. 4,132,120 describes a speed change pulley of the type comprising two oppositely and coaxially disposed side plates each having a frustoconical portion; one of the side plates is a movable side plate, under the bias of resilient return means and axially movable opposite the other side plate, or fixed side plate. The resilient return means comprises an annular member or diaphragm, having a peripheral portion which forms a resilient washer of the Belleville washer type which abuts against the movable side plate, and a central portion which is divided by slots into radial fingers which abuts against a component axially fast with the fixed side plate. Engagement means are provided on the diaphragm for cooperation with complementary opening means provided on the movable side plate, and comprise at least one engagement member forming a component formed separately from the diaphragm and suitably fitted thereon.
The essential function of such engagement members is to allow the relative centering of the movable side plate and the diaphragm with respect to each other without necessitating any local change in shape of the diaphragm which may lessen the strength thereof, increasing the diameter thereof. However, they may also function to allow the driving of the movable side plate in rotation by the diaphragm.